Measurement of the B0 --> pi l nu Form-Factor Shape and Branching Fraction, and Determination of |Vub| with a Loose Neutrino Reconstruction Technique

TL;DR

This study measures the B0 --> pi l nu decay form-factor shape and branching fraction using a novel neutrino reconstruction method, leading to a precise determination of |Vub| with implications for CKM matrix studies.

Contribution

It introduces an innovative loose neutrino reconstruction technique for semileptonic B decays, enabling detailed form-factor and |Vub| measurements with high statistical accuracy.

Findings

Branching fraction BF(B0 --> pi l nu) = (1.46 +- 0.07 +- 0.08) x 10^-4

Form-factor shape f+(q2) extracted from data

|Vub| determined as (4.1 +- 0.2 +- 0.2 +0.6-0.4) x 10^-3

Abstract

We report the results of a study of the exclusive charmless semileptonic decay, B --> pi l nu, undertaken with approximately 227 million BBbar pairs collected at the Upsilon(4S) resonance with the BaBar detector. The analysis uses events in which the signal B decays are reconstructed with an innovative loose neutrino reconstruction technique. We obtain partial branching fractions in 12 bins of q2, the momentum transfer squared, from which we extract the f+(q2) form-factor shape and the total branching fraction BF(B0 --> pi l nu) = (1.46 +- 0.07(stat) +- 0.08(syst)) x 10^-4. Based on a recent unquenched lattice QCD calculation of the form factor in the range q2 > 16 GeV^2, we find the magnitude of the CKM matrix element |Vub| to be (4.1 +- 0.2(stat) +- 0.2(syst) +0.6-0.4(FF)) x 10^-3, where the last uncertainty is due to the normalization of the form factor.